Adding objects in a different scene than controller's
You can't duplicate objects that are not present within the scene you want to have them in.

If they are not present already you might load them into the scene via LibLoad. I suggest to do that only when you need dynamic loading.

The easier way is to link the object (or mesh) from the original scene to the other scene. This means when you edit the object in either scene both objects get updated. Be aware: they are only linked in Blender not in the BGE. in the BGE they are two different objects.